In U.S. Pat. Nos. 6,352,952 and 6,670,415 (owned by W. R. Grace & Co.-Conn.), Jardine et al. disclosed that dosage efficiency of dispersants used in concrete can be diminished by the presence of clay. It was discovered that oxyalkylene polymers, used for dispersing cement particles within concrete, tended to be absorbed by clay particles that were born or conveyed by the sand and/or other aggregates used in making the concrete.
Jardine et al. proposed to mitigate this clay problem by deploying certain compounds, which, in the manner of sacrificial agents, became absorbed by the clay particles which would have otherwise absorbed the oxyalkylene cement dispersant molecules and rendered them unavailable to function as cement particle dispersant within the concrete mix.
The present inventors refer herein to clay activity-modifying agents, otherwise called clay mitigation agents, using the acronym “CMA(s).”
Jardine et al. taught that the order of addition of a CMA depended on the chemical nature of the CMA. Thus, if the CMA contained cation or polar organic molecules, the CMA was preferably added to the clay before water was introduced to the clay (See U.S. Pat. No. 6,670,415, Abstract, lines 14-16).
For CMAs having very high affinity for clay, such as quaternary amines (e.g., poly-quaternary amines), Jardine et al. described that such CMAs were to be added to the clay-bearing aggregate before, during, or after water was introduced (See U.S. Pat. No. 6,670,415 at Abstract, lines 16-20), and/or they could be added simultaneously with or before the cement dispersant was added (See U.S. Pat. No. 6,670,415 at col. 6, lines 48-58).
In U.S. Pat. No. 8,257,490 B2 (owned by Lafarge S. A.), Jacquet et al. taught the use of inerting agents which were preferably to be added to clay-bearing sand at the quarry or at the ready-mix plant, preferably to the sand first to prevent excessive use of a superplasticizer.
The concept of treating aggregates at quarries using CMAs was further emphasized in Ser. No. 14/395,603 (US Publ. No. 2015/0065614) and Ser. No. 14/378,158 (US Publ. No. 2015/0065614), co-owned by W. R. Grace & Co.-Conn.
Until the present invention, it was generally believed that the most effective mode for adding CMAs was directly onto clay-bearing aggregates either at the quarry or at the ready-mix plant before mixing the aggregate with water and/or cement dispersant. This separate and prior addition would avoid any competition between CMAs, on the one hand, and water and/or the cement dispersant on the other hand.
Even if the cement dispersant had far lower clay affinity compared to the CMAs, this separate and prior addition of CMAs was preferred because the over-riding objective was to maximize the rheological performance and strength of the concrete.
Also fundamental to the conventional thinking was the assumption that adsorption by the clay of CMAs is irreversible. It made sense, then, for purposes of expediting the concrete delivery process, to introduce the CMA first to the clay-bearing aggregate or concrete before introducing the cement dispersant into the concrete mix.
However, the present invention changes this conventional thinking in fundamentally unexpected ways.